The IP Multimedia Subsystem (IMS) is an architectural framework for delivering internet protocol (IP) multimedia to mobile users over various types of wireless and fixed networks. Through advancements in wireless access technologies, IP based communications for multimedia application services became available for various types of mobile devices. Subscribers of second and third generation mobile communication networks are offered application services which require access to special network subsystems such as the IMS. Examples of such application services include white board discussions, video conferencing, Push to talk over Cellular (PoC), Voice over IP (VoIP), real-time content sharing including video/audio files, instant messaging, interactive gaming, and the like. One of the challenges posed by IP multimedia application services is to provide a good user experience with media application services across a variety of computing and mobile devices running over diverse networks (e.g., different types of wireless networks, fixed networks, or the like).
As a mobile device roams beyond its home network, it may seek to access application services in other networks that it visits. For example, a mobile device in a cellular network may seek to access video chat application services delivered via the IMS. To enable roaming, communication networks must therefore identify and register home and visiting devices accessing the resources of the network. For example, a visiting network typically allows visiting mobile devices to establish IMS sessions. To access the IMS, mobile devices use a subscription provided by the home network of the mobile device. Once the mobile device visits a network, a registration procedure is initiated. To register with the visited network, the mobile device transmits a Uniform Resource Indicator (URI) that identifies the home network of the mobile device so that the subscription can be verified. Within the visited network, the Home Subscriber Server (HSS) manages the subscriptions of home and visiting subscribers.
Determining how to allow roaming access to IMS application services is a challenging problem for the telecommunications industry. At present, the 3rd Generation Partnership Project (3GPP) working group proposal is to maintain the location and address of each mobile device at each switch within the IP network. However, this solution requires significant network resources. In particular, the distributed method proposed by 3GPP requires the propagation of the mobile device addresses throughout the network, which is obviously expensive from a bandwidth/time perspective. An alternative solution that reduces the numerous data calls and messaging of the 3GPP proposal is therefore desired.